Determination of the infectious dose of Helicobacter pylori during primary and secondary infection in rhesus monkeys (Macaca mulatta).

We sought to determine the infectious dose of Helicobacter pylori during primary and secondary infection in the rhesus monkey and to determine whether preinoculation acid suppression is necessary to produce colonization. Mixed inoculation with three human-derived strains showed that H. pylori J166 is particularly adapted to colonization of rhesus monkeys, since it outcompeted two other strains. The minimum infectious dose of H. pylori J166 was 10(4) bacteria in specific-pathogen (H. pylori)-free monkeys. Rechallenge of these monkeys after antibiotic therapy was characterized by a 10- to 100-fold decrease in bacterial load compared to primary infection, but with little change in the infectious dose. Acid suppression prior to inoculation was not necessary for colonization to occur. These results provide a basis for future animal experiments using more ecologically relevant conditions of inoculation and suggest that reduction in bacterial load rather than complete protection may be a more realistic goal for H. pylori vaccination.